Earth-shield for transformers.



No 767,503. I PATBNTED AUG. 16, 1904. C. I. SCOTT.

EARTH SHIELD FOR TRANSFORMERS.

APPLICATION FILED SEPT. 16, 1903.

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ATTbRNEY UNITED STATES ."Patented August 16, 1904.

PATENT OEEIcE.

WESTINGHOUSE ELECTRIC & MAN UF TION OF PENNSYLVANIA.

CTURING COMPANY, A CORPORA- EARTH-SHIELD FOR TRANSFORMERS.

SPECIFICATION forming part of Letters Patent No. 767,503, dated August16, 1904. Application filed September 16, 1903- Serial No. 173,480. (Nomodel.)

T 0. whom, it may concern:

Be it known that 1, CHARLES F. Soon, a citizen of the United States, anda resident of Edgewood Park, in the county of Allegheny and State ofPennsylvania, have invented a new and useful Improvement inEarth-Shields for Transformers, of which the following is aspecification.

My invention relates to protective apparatus IQ for electricaltransformers; and it has for its object to provide simple and eflicientmeans for the prevention of heating of the grounded metallic shieldswhich are sometimes placed between the high and low voltage windings ofI5 such apparatus.

In the accompanying drawings, Figure 1 is a view in section through atransformer between a pair of primary and secondary coils; and Fig. 2 isa View in transverse section through a pair of adjacent primary andsecondary coils, showing a shield constructed in accordance with myinvention.

Grounded sheets of metal are sometimes placed between adjacent coilsbelonging, re- 2 5 spectively, to the primary and secondary windings ofa transformer, so that in case of accidental injury to or break down ofthe insulation the high-voltage current passes through the metallicshield to the ground, thus effec- 3 tually protecting the low-voltagewinding from the high-voltage currents. However, when such shields areemployed in transformers of the shell type considerable trouble is oftenexperienced on account of the heating 35, of these shields by localeddy-currents generated therein. This difliculty I have avoided bysplitting the shields in those places where the eddy-currents are mostlikely to occur or by providing a shield the resistance of which 4 issuch as to prevent excessive currents.

Referring to the drawings, a metallic shield 1 is placed between thehigh and low tension coils 2 and 3 and is of substantially the sameoutline as the coils. It is placed between the sheets of non-conductingmaterial 4, which separate and insulate the high and low voltage coilsfrom each other. In order that the shield may not form a short-circuitedturn around the magnetic circuit 5, I provide breaks 6 in the metallicsheet at one or more places and 5 separate and insulate the portionsfrom each other at such point or points.

In that portion of the shield which is surrounded directly by the ironcore 7 there is little tendency for local eddy-currents to circulate;but at the ends of the coils there is a considerable firm, which passesthrough the metallic sheet at angles thereto and produces localeddy-currents therein. In order to prevent such eddycurrents,I split themetallic shield 1 at the ends of the coils into a plurality of narrowtransverse strips 8 and insulate adjacent strips from each other byintroducing properly-shaped sheets of non-conducting material 9, asindicated in Fig. 2. It is evi- 5 dent that in this manner the localeddy-currents are kept down to a safe value, that very little heating ofthe shields is likely to occur, and that the waste energy from thiscause hecomes a minimum. 7

If desired, the shields may be made of any suitable high-resistancematerial, such as German silver, in which case the splitting of theshields into transverse strips at the ends of the coils may be dispensedwith, if desired.

Although I have shown a shield in connection with only one pair ofadjacent high and low voltage coils, it is to be understood that similarshields may be employed between all pairs of such coils.

I claim as my invention 1. Protective apparatus for transformers havinga plurality of coils and a magnetic circuit, comprising grounded sheetsof high-resistance conducting material placed between 5 adjacent coils,the resistances of said sheets being such as to reduce the eddy-currentstherein to a safe value.

2. Protective apparatus for transformers having a plurality of coils anda magnetic cir- 9 cuit, comprising grounded sheets of conductingmaterial placed between adjacent coils, the portions of the said sheetsnot directly sur rounded by the magnetic circuit being subdividerfto soincrease the resistance as to reduce the eddy-currents to safe values.

3. Protective apparatus for transformers having a plurality of coils anda magnetic circuit comprising grounded sheets of metal which are placedbetween adjacent primary and secondary coils, said sheets having thoseportions not directly surrounded by the magnetic circuit split into aplurality of strips, and non-conducting material for separating adjacentstrips.

a. Protective apparatus for transformers having a plurality of coils anda magnetic circuit comprising grounded sheets of metal which are placedbetween adjacent primary and secondary coils, portions of said sheetsbeing split into a plurality of strips, and nonscribed my name this lstday of September, 1903.

CHAS. F. SCOTT.

Witnesses: 4

J. C. DIECKMANN, BIRNEY HINES.

